With few exceptions, all prior arts teaching the construction and operation of a parallel bank of electronic filters for conditioning electrical signals in flowmeters, particularly vortex flowmeters, employ the well known and routinely practiced feedback method to control the switching of a plurality of filters included in the parallel bank of filters. In other words, the output of the parallel bank of filters is fed back to a filter control device switching on and off the individual filters included in the parallel bank of filters in such a way that only one individual filter best suited to selectively transmit the flow signal excluding the noise is switched on at one time. Generally, the above-described feedback method controlling the switching of individual filters included in the parallel bank of filters does not work in conditioning the flow signal of very low amplitude such as an alternating electrical signal generated by vortex shedding at very low velocities of fluid flow or in a high noise environment where the noise signals are dominant in frequency or amplitude because the parallel bank of filters controlled by the feedback command signal locks on to the noise signal created by mechanical vibrations of the vortex flowmeter body rather than on the weaker vortex signal. The parent patent application Ser. No. 08/113,197 discloses a compound electronic filter that overcomes the problem and difficulty existing with the prior arts, in which compound electronic filter the switching of individual filters included in a parallel bank of filters is controlled by a command signal generated by the frequency of the alternating electrical signal detected at the input end of the parallel bank of filters instead of the output end thereof wherein the alternating electrical signal providing the command signal is filtered by a parallel bank of a few prefilters controlled by a command signal generated by the frequency of the alternating electrical signal detected at the output end of the prefilters.